1. Field of Invention
In practice, the sulfonation of organic compounds by reaction with sulfur trioxide (SO.sub.3) comprises in particular reactions of the sulfonation and/or sulfatization type, of which the reaction scheme is known and may be re-presented as follows: EQU sulfonation: R--H+SO.sub.3 .fwdarw.RSO.sub.3 H EQU sulfatization: R--OH+SO.sub.3 .fwdarw.ROSO.sub.3 H
Reactions of this type are distinguished by very fast kinetics, but are also burdened by the release of considerable heat of reaction which can amount, for example, to between 100 and 180 kJ/mol. In reaction systems of comparatively high viscosity, this presents heat dissipation problems, so that local overreactions, overheating, carbonization, dehydration and/or polymerization can often be initiated. Oxidation reactions initiate discoloration which adversely affects the quality of the reaction products, so that the sulfonation and/or sulfatization products generally have to be bleached and purified.
2. Statement of Related Art
Among the technical embodiments of these reactions, a gasliquid reaction with gaseous sulfur trioxide, diluted in an inert gas, on thin liquid films occupies a prominent position
Although, in many cases, organic compounds can be sulfonated and/or sulfatized under relatively mild reaction conditions by using chlorosulfonic acid, sulfuric acid or oleum instead of sulfur trioxide, the hydrogen chloride given off or the sulfuric acid formed have to be separated with considerable effort. Finally, many particularly sensitive substrates cannot be satisfactorily sulfonated and/or sulfatized with conventional agents.
To reduce, if not completely eliminate, these disadvantages during the sulfonation and/or sulfatization reaction, attempts have been made to reduce the extreme reactivity of sulfur trioxide by addition of solvents. The use of solvents provides for better distribution and admixture of the reactants and, easier heat dissipation, for isothermal conduct of the reaction (see for example E. E. Gilbert in "Chemical Reviews" 62, 549 to 580 (1962); Kirk-Othmer in "Encyclopedia of Chemical Technology" 22, 1 to 45 (1983).
Sulfur dioxide or halogenated hydrocarbons for example have been proposed as solvents. The use of liquid sulfur dioxide, which is toxic and highly corrosive, involves handling problems and, in addition, is applicable only to reactions involving relatively non-sensitive aromatics. The other solvents proposed for sulfur trioxide, such as low-boiling halogenated hydrocarbons, paraffins, cyclic ethers and also tertiary amines, can also give rise to considerable difficulties. Solvents of this type can produce violent reactions with SO.sub.3. On completion of sulfonation and/or sulfatization, secondary reaction products formed during preparation of the sulfonating and/or sulfatizing agent have to be separated generally with difficulty in addition to the solvent.
The object of the present invention is to provide a safe and comparatively non-sensitive reaction medium, present in the liquid phase under the reaction conditions for the sulfonation of organic components with SO.sub.3, which provides for improved monitoring and control of the reaction to such an extent that unwanted secondary reactions can be substantially or even completely eliminated. Accordingly, the invention makes known sulfonation reactions of the type mentioned easier to control. The process of the invention makes it possible to carryout specific sulfonation reactions on highly sensitive substrates which, hitherto, could not be considered for sulfonation with SO.sub.3.